Two stand out for me.

Back in 1976 (in the days before most people did home inspections as a
part of the buying process), my parents bought a "handyman special"
and it was a treat. There was a window a/c unit in the family room
plugged into an outlet we thought was running 220v. The a/c unit
didn't work, so we went to trace the wire to see what circuit it was
on and discovered they'd daisy-chained a couple of household extension
cords from the breaker box through the crawlspace and up behind the
baseboard radiator, cut off the multi-outlet block at the end of the
second cord and attached a 220 box.

In 2005 my wife and I bought a row house in our neighborhood to fix up
and rent out. In the basement the owner had put up a wall to divide
the back part (workroom, weirdly large powder room) from the front.
He'd used 2x4s to frame the wall, but then instead of putting up
drywall he'd just stapled that corrugated paper brick up - you know,
the type of stuff they used to use in the cheesy fake fireplace
Christmas decorations.